Coating surfaces of zinc-base



Patented Dec. 21, 1938 PATENT OFFICE coarme summers or zmc-nssr:

William E. Hall, Hillside, N. 1., assignor to The Egyptian lacquer Manufacturing Company, a corporation of New Jersey No Drawing. Applic ation April 28, 1937,

Serial Nil 139,456

10 Claims. (Cl. 13439) This invention relates to coating metallic surfaces, especially surfaces of zinc-base. By zincbase I mean zinc, cadinium, or magnesium or alloys of these elements in which zinc or cadmium or magnesium or two or three of these elements constitute a major ingredient. The invention is adapted for coating galvanized surfaces and the like and contemplates particularly the production of decorative and protective coatings on sheet metal products such as galvanized iron rooilng'or shingles.

This application is a continuation in part of my co-pending application Serial No.-l03,i62,

filedSeptember 30,1936.

Galvanized iron surfaces tend to tarnish and corrode upon exposure to the weather and leave much to be desired-from the standpoints of appearance and durability unless subjected-to further treatment. Consequently it has been heretofore customary practice to paint the galvanized metal either before or after it is in place. Paint tends to peel after a short time of service when applied to untreated galvanized surfaces so that it has been proposed heretofore to etch or sandblast the galvanized surfaces preparatory to applying the paint. Etching, however, 1 has not proved entirely satisfactory because zinc, and particularly zinc in crystalline form on galvanized surfaces, tends to etch in an irregular and spotty manner which deleteriously affects both the appearance and the resistance to weather of the .inished surface. I

Sprayapplication of primer and paint to galvanized metal, especially galvanized metal roofing which is coated at the factory in large lots, is

highly desirable because of the resultant saving in labor. But efforts to employ the heretofore customary etching agents or primers, such as aqueous solutions of hydrochloric acid, to the galvanized metal by means of sprays has only aggravated the aforementioned difllculties. when applied with sprays such primers do not flow uniformly over the galvanized roofing but tend to collect as isolateddroplets. Etching occurs immediately adjacent the droplets but, unless an excessive amount of primer is sprayed on, much of the surface area remains unetched while other portions are excessively corroded. .When the surface is etched in this uneven manner, the lack of uniformity in appearance persists even after the surface is painted, probably because the more deeply etched surfaces absorb more of the paint vehicle than other portions and form spots which have less'lustre'than adjacent areas. Such spots of lower lustre are similar in appearance to those known as "hot spots on a plaster wall which has been painted without proper priming.

Brush application of the heretofore customary primers has yielded fair results, but unless much time and effort is spent in working the primer over the surface, the primed surface is spotty and the spotty character persists after the surface is painted, injuring its appearance and decreasing its resistance to weathering.

As a result of my investigations I have discovered a coating composition or primer for surfaces of zinc-base such as galvanized metal which not only gives excellent results when applied by spraying and entirely avoids the dimculties due to the spotty finish of prior primers, but also imparts to the surface a uniform and durable finish of any desired color and shade. This finish is not aifected substantially under the conditions to which ordinary roofing is exposed. Tests indicate that the finish given by the priming treatment of my invention will last for many years even when ment of paint'is placed over the primed surface. However, since the priming treatment of my invention places the galvanized metal in excellent condition to receive and retain paint, I prefer, especially in the caseof galvanized roofing, to use both paint and, primer, employing a primer which imparts to the roofing the same color as the subsequently applied paint, thus increasing the protection afforded to the roofing. Eventually the paint may come off the roofing in more exposed portions thereof, but inasmuch as the priming treatment has imparted the same or nearly the same appearance to the underlying galvanized surface, re-painting is necessary at infrequent intervals, if at all, and the roofing never acquires the leprous appearance often acquired by ordinary painted galvanized iron.

The primer of my invention comprises a mixture containing water, a water-soluble etching agent for zinc-base surfaces, a readily volatile, non-viscous, water-miscible organic liquid which wets the zinc-base surface more easily than does water and which does not react readily with the aqueous solution of the etching agent in the primer, and a pigment in the form of a waterinsoluble compound of a heavy metal which does, not react readily with the aqueous solution of the etching agent in the primer.

I prefer to-employ hydrochloric acid as the The readily volatile, water-miscible and nonviscous organic liquid in the primer acts as a wetting agent. I have found that acetone, methyl ethyl ketone, mono-ethyl ether of ethylene glycol and the common lower alcohols such as methyl alcohol, ethyl alcohol and propyl a1- cohol are among the most satisfactory wetting agents to employ in the practice of my invention.

I prefer to use mineral pigments in the primer of my invention. By mineral pigmen I mean finely divided, water-insoluble compounds of heavy metals (both natural and synthetic) such as the oxides of iron, chromium and titanium, barium sulphate, and complex pigments such as lithopone and titanated lithopone.

As indicated hereinbefore, the pigment employed should not be one which will be dissolved in large part by the aqueous solution of the etching agent in the primer under normal conditions of storage and use. Thus inert pigments such-as barium sulphate are satisfactory, although I prefer to use pigments which are substantially insoluble in the aqueous solution of the etching agent in the primer. The oxides of iron, titanium and chromium (although not completely inert to the action of the mineral acids) are more satisfactory than inert pigments, because they become more'flrmly affixed to the treated surface. This I believe to be due to the fact that slight reaction between the etching agent and the pigment aids in fastening the latter to the treated surface. This may be due either to a cementing action of the reaction products formed or it may be due to an alteration of the surface of the pigment particles which makes them adhere more firmly to zinc-base surfaces.

In addition to water, the etching agent, the wetting agent and the pigment, the primer of my invention preferably contains two other ingredients-a deposition agent and a greasecutting agent. I

By deposition agent" I meana water-soluble salt ofa metal less electro-"positive than zinc, such as copper sulphate, in which the metal, for example copper, tends to replace zinc and deposit on the zinc-base metal surface. The use of this depositiomagentis not essential but aids in obtaining a uniform surface for the application of paint.

Practically all galvanized iron and other fabricated forms of zinc-base metal have a thin non-uniform and usually invisible film of oil or grease upon them (at least in patches) which has attached to the metal during fabrication or during subsequent handling. In order for the primer to act upon the metal surface it is necessary that it penetrate or remove this film of grease or oil. Otherwise the film will interfere with uniform etching. The grease-cutting agent enables the primer to penetrate the film. The agent should be an organic solvent for hydrocarbons of the parafiln series. In addition it must be miscible with the wetting agent in the primer. Toluol, carbon tetrachloride and their homologues are preferred examples of greasecutting agents to be employed.

In practically all industrial applications it is safer to include the grease-cutting agent in the primer of my invention. If, however, it is certain that the metal surface to be treated has no grease or oil on it, the grease-cutting agent may be eliminated from the primer and replaced by an equal volume of wetting agent.

, It is necessary that all of the ingredients employed in the primer be compatible with'each other in the final mixture. Thus the wetting agent selected must be a solvent both for water and the grease-cutting agent. Otherwise, the various liquids will separate out in layers, greatly impairing the eifectiveness of the primer. Ethyl alcohol, for example, is soluble both in water and in carbon tetrachloride or toluol. It therefore acts not only as a wetting agent but also as a so-called blending agent for the water and carbon tetrachloride or toluol which are not mutually soluble.

The action of the wetting agent in the practice of my invention is believed to be somewhat analogous to the action of a flotation agent in ore dressing. Mineral particles having metallic surfaces are water-repellant but are wetted by flotation agents. Consequently when a mixture of mineral particles some of which have non-metallic surfaces (quartz, feldspar) and others of which have metallic surfaces (pyrite, galena) are agitated vigorously in the presence of water and a flotation agent (pine oil), the fiotation agent attaches to the particles having metallic surfaces and to air bubbles resulting from the agitation and are thus buoyed up in a froth which is easily skimmed.

Zinc-base metal surfaces have a greasy quality even when they are absolutely clean. In other words, such surfaces are water-repellant. In consequence, when a strictly aqueous liquid is sprayed on such a surface it tends to collect thereon as minute drops and does not'tend to spread into a uniform film. This is especially true of galvanized sheets and the like where the coarsely crystalline character of the metal makes the surface irregular and bumpy, and thus introduces a further obstacle to the flow or spread of the drops over the surface.

However, when a suitable wetting agent for zinc-base metals is included in the sprayed liq-- This results in an even distribution and an intimate relationship between the etching agent in the aqueous solution and the pigment particles, with the result that the metal surface is etched uniformly.

I believe that the wetting agent in the primer,

in addition to overcoming the difficulties described hereinbefore in a manner analogous to that of a flotation agent in ore dressing, also aids in dispersing the pigments in the primer. This is manifested by the tendency of the pigmented primer of my invention to become smooth with much less stirring than is required with a suspension of pigments in a fluid which does not contain a wetting agent. The improved dispersion of pigments in the primer of my invention may be due to the more thorough wetting of the pigments by the fluids, but whatever be the explanation, the improved dispersion which is attained'in the practice of my invention facilitates the uniform application of the primer by spraying and precludes the presence of large agglomerates of pigment particles.

Apparently, during the etching process the pigment particles become affixed to the surface. I believe that the adhesion of the pigment particles to the metal surface without any conventional film forming ingredients to hold them there is due to adsorption. In any case, the fact remains that the pigment particles become affixed to the sur-- face even in the absence of any of the customary film forming ingredients such as nitrocellulose or linseed oil.

My invention will be more completely understood if reference is made to the following detailed description of my presently preferred practice.

Preparation of the primer I first make up a clear primer which contains:

The clear primer may be made up conveniently in 100 gallon batches in which case the parts by volume in the above formula may be taken as gallons. No special procedure is necessary in making up the clear primer. The ingredients are simply mixed together vigorously for a period of about 15 minutes, preferably in anacid-proof vessel.

The proportions of ingredients in the clear primer for summer conditions may be varied within moderately wide limits without impairing the final results. In general, however, the total volume of water, etching agent and deposition agent should range from 5 to 10% of the total.

The wetting agents should comprise from 60 to 75% of the total volume, and the grease-cutting agents should be about 25 to 35% of the total volume. In this connection it should be noted that the mono-ethyl ether of ethylene glycol is one of the most desirable wetting agents to incorporate, to some extent at least, in the primer because it acts as a blending agent for the other liquid ingredients and permits a wider variation in the proportions of the other liquid ingredients in the primer.

I The clear primer of Formula I is satisfactory when it is used soon after preparation or if it is stored for a considerable period at temperatures which prevail during the summer months. However, during storage in cold weather the primer of I Formula I tends to segregate. I have discovered that this segregation does not occur when the clear primer is made according to the following formula:

I'bmm II Ingredients Gallons Denatured ethyl alcohol 01% p ellosolve, mono-ethyl ether of ethylene glycol..-.-.- 3

0 lm 307 cop r sulphate solution i. e. 8% lbs. of Gus 0 .5Hr0

in 3 gamns of water 3% Commercial concentrated hydrochloric acid (containing about 35% by weight H01 5 I prefer to mix the ingredients in Formula 11 in the order in which they are given, although this is not essential.

It will be noted that Formula II (the cold weather primer) differs from Formula I in that it contains no carbon tetrachloride and five parts less by volume of toluol, the shortage of these substances being made up of denatured alcohol.

The allowable variation in the proportion of ingredients in the clear primer for winter conditions is somewhat less than in the case of primer which is made up, stored and used during warm weather. Thus, it is not advisable to vary the proportions of the "cold weather primer outside of the following ranges:

To the clear primer is added the mineral pig- Percent of total volume Sum of water, etching agent and deposition agent (not including water present in denatured alcohol) 7% to 12 /2 Wetting-agents to Grease-cutting agents 18 to 25 ments to give the desired color to the treated surface. The pigment should be acid-resistant and for optimum results it should be fine enough to pass completely through a screen having 325 meshes to the inch. In general the mineral oxide pigments such as chrome green, red iron oxide, black iron oxide'and titanium dioxide are to be preferred, but acid resistant sulphates such as barium sulphate and compound pigments such as lithopone and titanated llthopone may be employed advantageously. The following tabulation gives the preferred proportions of some pigments to clear primer:

Ounces of dry D ll PB! 0010' Pigments gallon of clear primer Green Chrome oxide 10 Red ma iron oxide 3 Black Black iron oxide s lack iron oxide 6 1 l itanium dixoide. 2 8

Red iron oxide 6 {Chrome oxide a 9 In mixing the clear primer and the pigment the latter is first worked into a paste with a small proportion of the primer. Working is continued until the paste is uniform and free of lumps, after which the balance of the primer is added and the whole is stirred together until the mixture is uniform and of a thin consistency.

Coating the metal surfaces The pigmented primer may be applied by brushing or by dipping, but spray application is preferable. My invention, therefore, contemplates a' process for producing a protective coating on a surface of zinc-base which comprises spraying the surface with a fluid mixture containing water, mineral acid, a mineral pigment and a volatile non-viscous and water-miscible organic liquid which does not react readily with the aqueous solution of themineral acid in the mixture and which wets the surface of zinc-base more easily than does water, and permitting the surface to dry, whereby the surface becomes etched with substantial uniformity and the pigment adheres thereto.

During the spray application of the fluid mixture, the pigment should be kept in suspension. This is preferably accomplished by agitating the fluid mixture in the reservoir which fills the spray.

Preferably also, the grease-cutting agent or the deposition agent hereinbefore described are included in the fluid mixture which is sprayed.

In greater detail, the application of the pigmented primer to the zinc-base metal surface, for example galvanized sheet iron shingles, should be conducted as follows:

Any visible grease or oil spots on the surface of the shingles is first removed by washing with an appropriate solvent such as naphtha. v

The pigmented primer is charged into an acid proof container, such as a wooden keg, equipped with an agitator and acting as a reservoir for a pneumatic spray gun having an acid proof nozzle and needle. The pigmented primer in the reservoir should be agitated throughout the period of spray application.

The clean shingle surface is then sprayed as uniformly as possible. The spray should be fine and evenly distributed in a fan shape. With the customary paint spray gun the air pressure when thespray is open should be approximately 40 pounds, and the valve which supplies the pig-' mented primer to the spray should be opened "only slightly; otherwise an excessive spray results. The sprayed coat of primer while wet should show definitely the pattern of the span-. 'gles on the'surface of the galvanized shingles.

' when the humidity is exceptionally high this drying period should be prolonged up to a maximum of about 24 hours.

One spray coat of primer is sufilcient, .but in no case should paint be applied over the primer surface until it is completely dry. One gallon of the primer will cover 450 to 500 square feet of surface if the primer is properly applied.

The containers, spray pots, spray guns and hose which are used for applying the primer should not be used for any other, purpose, such as for spraying paint.

When changing from one color of primer to another, the interior of the entire spray apparatus should be cleaned with water.

As hereinbefore indicated, it is not necessary to apply paint over the primed surface because the primer itself imparts to the roofing a'durable coating of any desired color or shade. However,

the primed surface furnishes an excellent base' for paint, particularly for the paint described hereinafter and presents an outstanding advantage over primers proposed heretofore in that paint can be applied directly over the dry primer coat, without first washing the primed surface or otherwise treating itto remove reaction products. tion for the surface I prefer to apply at least one spray coat of paint over the primed surface, usingpaint of the same color as the pigmented primer. The paint gradually challrs" from the surface during exposureto the weather, but even after the paint is entirely gone the roof will still give many years of service and will appear substantially unaltered incolor bothduring the time when the paint is chalking off and thereafter.

Almost any paint may be used to cover the primedishinglepsurface, However, I have discovered that it is best to employ paint which chalks when exposed to the weather, i.= e. paint which fails gradually and washes of! the painted Consequently, to give additional protec .Of heavy D surface as an impalpable powder or mud during long periods of exposure. A paint of this character is desirable because it does not fail in patches and therefore gives additional security that the roof will not acquire a spotty appearance due to the fact that on some portions of it paint still remains while on other portions the paint has been removed, exposing a primed surface which is of slightly different appearance.

I have developed an especially suitable paint which comprises a varnish base made by cooking China wood oil with a phenol formaldehyde resin together with a high proportion of filler" such as talc or barytes. This paint is especially applicable in the practice .of my invention not only because it does not fail in patches but also because it adheres well to the primed surface and gives an unusually uniform finish. 1

-The varnish is prepared by cooking about 4 parts by weight of phenol formaldehyde resin with about 16 parts by weight of China-wood oil for about half an hour at a temperature not to exceed 480 F. The mixture thus formed is allowed to cool and 26 parts by weight of mineral spirits is mixed with it thereafter. About 1 part by weight of dryer (for example a mixture of powdered cobalt, manganese and lead in the proportion 4-16-80 by weight) is then added to the varnish.

The pigment employed in the paint should be the same in fineness and color as the pigment in the primer. However, the chemical composition of the pigment in the paint need not be the same as that in the primer because the pigment in the paint need not be acid resistant to the same degree. Thus, when green shingles are desired, chrome green should be used as the pigment in the primer, but a mixture of Prussian blue and lead chromate which will give the same shade and color of green may be used in the paint.

A preferred formula for the paint to apply over the primed surface is as follows:

A portion of the varnish is used as a grinding medium for the pigment and filler. Grinding may be carried out conveniently in a pebble mill or the like. A stiff paste is thus formed. Thereafte'rthe balance of the liquid ingredients of the paint is added.

The above produces approximately 178 gallons Before use this should be thinned with one part of naphtha or mineral thinner for each three parts of the paint.

The thinned paint should be applied. over the dry primed surface with an ordinary pneumatic spray gun, using sufflcient paint to cover the surface adequately. It has been found that one gallon of the paint described hereinbefore will adequately 'cover about 400 square feet. Only one coat of this paint is necessary.

Good results have been obtained with an air pressure of from 30 to 40 pounds per square inch when the gun is open and with the paint valve on the gun open but slightly so as to produce a fine spray.

After painting, the finished articles should be.

dried for at least 24 hours before they are packed for shipment. The paint described above acquires a fiat and dry appearance within a few minutes after it is applied, but it does not harden to the extent required for handling until it has dried at room temperature for at least 12- hours.

Care should be taken to assure that the primed surface is absolutely dry before paint is applied over it and also to assure that the paint does not come in contact with the wet primer at any time. This means that the containers, hose, spray gun and any other apparatus with which the paint comes in contact should not be used for handling the primer.

I claim:

1. A priming composition for surfaces of zincbase free from film-forming ingredients comprising as a liquid vehicle an inorganic etching acid,

water, and at least one water-miscible organic liquid which wets the zinc-base surface more readily than does water and which does not react readily with the aqueous solution of said inorganic etching acid, said wetting agent constituting a major portion of said vehicle, and a finely divided water-insoluble mineral pigment resistant to attack by said etching acid, said pigment being present in amount sufllcient to coat the surface of the zinc-base to which the priming composition is applied. i

2. A priming composition for surfaces of zincbase free from film-forming ingredients compris ing as a liquid vehicle an inorganic etching acid, water, and at least one water-miscible organic liquid which wets the zinc-base surface more readily than does water and which does not react readily with the aqueous solution of said etching' acid, said wetting agent constituting a major portion of said vehicle, and a finely divided pigment in the form of water-insoluble oxide of a heavy metal resistant to attack by said etching acid and being present in amount sufficient to coat the surface of the zinc-base to which the priming composition is applied.

3. A priming composition for surfaces of zincbase free from film-forming ingredients comprising as a liquid vehicle an inorganic etching acid,

water, at least one water-miscible organic liquid which wets the zinc-base surface more-readily than does water and whichv does not react readily with the aqueous solution of said etching acid, and an organic solvent for paraifin'hydrocarbons which is miscible with the Wetting agent, said wetting agent constituting a majorportion of said vehicle, and a finely divided water-insoluble mineral pigment resistant to attack by said etching acid and being present in amount sufficient to coat the surface of the zinc-base to which the priming composition is applied.

4'. A priming composition for surfaces of zinc base free from film-forming ingredients comprising as a liquid vehicle an inorganic etching acid,

water, and at least one water-miscible organic liquid which wets the zinc-base surface more readily than does water and which does not react readily with the aqueous solution of said etching acid, said wetting agent constituting a major portion of said vehicle, a water-soluble salt of a heavy metal which is less electro-positive than.

the zinc-base metal, and a finely divided waterinsoluble mineral pigment resistant to attack by said etching acid and being present in amount suflicient to coat the surface of the zinc-base to which the priming composition is applied.

5. A priming composition for surfaces of zincbase free from film-forming ingredients comprising as a liquid vehicle hydrochloric acid, water, and at least one water-miscible organic liquid which wets the zinc-base surface more readily than does water and which does not react readily with the aqueous solution of hydrochloric acid, said wetting agent constituting a major portion of said vehicle and a finely divided water-insoluble mineral pigment resistant to attack by the hydrochloric acid and being present in amount suflicient tocoat the surface of the zinc-base to which the priming composition is applied.

6. A priming composition for surfaces of zincbase free from film-forming ingredients comprising as a liquid vehicle an inorganic etching acid, water, and at least one water-miscible organic liquid which wets the zinc base surface more readily than-does water and which does not react readily with the aqueous solution of said etching acid, said organic liquid being selected from the.

group consisting of methyl alcohol, ethyl alcohol, propyl alcohol, acetone, methyl ethyl ketone and mono-ethyl ether of ethylene glycol, said wetting agent constituting a major portion of said vehicle and a finely divided water-insoluble'mineral pigment resistant to attack by said etching acid and being present in amount sufiicient to coat the surface of the zinc-base to which the priming composition is applied.

'7. Apriming composition for surfaces of zincbase free from film-forming ingredients comprising as a liquid vehicle hydrochloric acid, water, at least one water-miscible organic liquid which wets the zinc-base surface more readily than does water and which does not react readily with the aqueous solution of hydrochloric acid, said Wetting agent constituting a major portion of said vehicle, and an organic solvent for parafiin hydrocarbons which is miscible with the Wetting agent,

said organic solvent being selected from the group consisting of carbon tetrachloride, toluol and homologues of these compounds, and a finely divided water-miscible mineral pigment resistant to attackby the hydrochloric acid and being present in amount suflicient to coat the surface -of the zinc-base to which the priming composition toluol, mono-ethyl ether of ethylene glycol, ethyl alcohol and a water-insoluble mineral pigment resistant to attack by said etching acid and being present in amount sufiicient to coat the sur faces of the zinc-base to which the priming composition is applied, said mono-ethyl ether of 'ethyleneglycol and said ethyl alcohol constituting a major portion of the liquid components of the priming composition.

10. A priming composition for surfaces of zincbase which consists of about 3 parts by volume of aqueous copper sulphate solution, about 5 parts byvolume of hydrochloric acid, about 20 parts by volume of toluol, about ,10 parts by volume-of mono-ethyl ether of'ethylene glycol, about 62 parts by volume of denatured alcohol, and a pigment in the form of a substantially water-insoluble oxideof a heavy metal selected from the group consisting of chromium, iron, titanium and zinc.

WILLIAM E. HALL. 

